1. Field of the Invention
The present invention relates to a method of preparing composite particles which can be applied to a spacer for use in electronic equipment, and used as a filler in a separating column, as a molding material, as a coating material, and as microspheres used in immunoassay methods in the medical field; and a method of preparing toner particles capable of developing latent electrostatic images in the field of electrophotography, electrostatic recording or electrostatic printing.
2. Discussion of Background
In the electrophotographic process or electrostatic recording process, a latent electrostatic image is formed on a latent-electrostatic-image bearing member such as a photoconductor or a dielectric material and developed into a visible toner image by a toner. This toner, which is pulverized to an appropriate size and charged to a predetermined polarity, is regulated to form a thin film on a toner-supply-roller such as a development sleeve with the aid of a blade in a development unit. The toner image thus obtained is transferred to an image-receiving medium such as a sheet of paper or a plastic film when necessary. The transferred image is then fixed on the image-receiving medium by heating or by applying a solvent vapor. A copy image can thus be obtained.
In the above-mentioned image fixing step, an adherent fusing system using a heat-application roller is commonly used in the electrophotographic copiers. This system has the shortcoming that the fused toner which is transferred to the image-receiving medium adheres to the surface of the heat-application roller and this toner adhering to the roller is again transferred to the image-receiving medium, causing the image-receiving medium to become stained with toner. Namely, the so-called off-set phenomenon occurs. To prevent the off-set phenomenon, a toner comprising a releasing agent is conventionally known, as disclosed in Japanese Patent Publication 52-3304. To prepare such a toner, a mixture of a binder resin, releasing agent, and other additives is kneaded while heated to the melting point of the binder resin, and then cooled and pulverized.
In the above case, it is required to thoroughly knead the mixture because the compatibility of the binder resin with the releasing agent is very poor. Insufficient kneading causes phase-separation, thereby producing a dispersed phase and a continuous phase in each toner particle. When the dispersed phase comprising the releasing agent becomes large, filming of the toner on the photoconductor and the development sleeve, and adhesion to a carrier are caused. The kneading time required to prevent the above-mentioned phase-separation problem is 5 times or more the kneading time in the case of the preparation of a toner not comprising the releasing agent.
To solve the aforementioned problems on the releasing agent, Japanese Laid-Open Patent Application 63-300245 discloses a method for preparing a toner. According to this method, finely-divided particles of the releasing agent are caused to adhere only to the surface of dyed matrix resin particles in such a way that these dyed matrix resin particles are mixed with an emulsion in which the releasing agent is dispersed by use of a surface active agent. In general, however, the emulsified releasing agent can be maintained in a stable condition owing to the large quantity of the surface active agent, so that the finely-divided particles of the releasing agent cannot be uniformly attached to the, surface of the matrix resin particles in the dispersion merely by mixing the emulsion of the finely-divided particles of the releasing agent and the matrix resin particles. In addition, even though the particles of the releasing agent adhere to the matrix resin particles, the releasing agent particles readily separate from the matrix particles, because the adhesion of the finely-divided particles of the releasing agent to the matrix resin particles is poor.